Space Weather Explained

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I was asked to explain the various sources for Space Weather. So here we go:

Solar Activity or Space Weather?

Solar activity describes events that take place on the sun, while space weather describes the change in solar activity as seen on our planet, by technology, and in the magnetic organization of the solar system.

Coronal Mass Ejections:

A Coronal Mass Ejection (CME) occurs when a prominence suspended above the surface of the Sun erupts and sends millions of tons of material into space. This cloud of charged particles is generally confined within a magnetic field (like a magnetic bubble), expanding and traveling out through the solar system at speeds from about 200 km/s up to a staggering 2000 km/s. When directed toward Earth, a CME typically arrives 2-3 days after eruption but in exceptional cases can arrive in less than 24 hours.

Solar Flares:

A solar flare is a bright flash of X-rays seen during an energetic explosion in an active region of the Sun. It’s usually seen as a large burst of X-rays, but may also have a coincident bright flash of white light. A flare lasts a matter of minutes but releases an immense amount of energy. During solar flares the sun can be 1000 times brighter in X-rays than usual.

High-speed Streams in the Solar Wind:

A high-speed stream (HSS) is like a powerful gust in the solar wind. Near the edges of a HSS are regions of high particle density and strong magnetic fields, while inside the stream the density and field are low and the temperature and velocity are high. The flow velocity inside a HSS can reach 300 to 1000 km/s. In some cases they will produce interplanetary shocks. A HSS comes from a coronal hole, a dark region in the solar corona, and is most common during the declining phase of the solar cycle. A HSS can last a long time: we often see a HSS every 27 days as its home coronal hole rotates into the right position.

Aurora Credit: Jeffrey R. Hapeman of Lac du Flambeau, Wis.

Geomagnetic Storms:

Earth’s magnetosphere is a bubble created around us by our magnetic field, which protects us from most of the particles the Sun throws at us. When a CME or high- speed stream arrives at Earth, it buffets the magnetosphere. If the arriving solar magnetic field is directed southward, it interacts strongly with Earth’s oppositely oriented magnetic field. As a result, Earth’s magnetic field is peeled open like an onion, allowing energetic solar wind particles to stream down the field lines to hit the atmosphere over the poles. At Earth’s surface, a magnetic storm is seen as a rapid drop in Earth’s magnetic field strength (typically a drop of 30 to 500 nT in 1-2 hours). This decrease lasts about 6 to 12 hours, after which the magnetic field gradually recovers over a period of several days.

Galactic Cosmic Rays:

A constant rain of galactic cosmic rays (GCRs) passes through all of space. These charged particles are accelerated to extremely high energies by galactic events such as supernovae (the catastrophic collapse of a star), although some may come from outside the Milky Way. Their high energy allows GCRs to penetrate through Earth’s magnetosphere and deep into the atmosphere. As they enter the atmosphere, they collide with molecules of oxygen and nitrogen and produce millions of tiny fragments. The GCR ionization rate (roughly the radiation dose) reaches a maximum at an altitude of about 12 km (40,000 ft) and then decreases toward Earth’s surface. The intensity of GCRs at Earth is highest during solar minimum. This happens because the intense regions of magnetic field extending out from the sun into the solar system during solar maximum divert the charged cosmic rays away from the solar system. As a result, the GCR intensity at Earth during solar maximum is half the GCR intensity during solar minimum.

Main Photo Credit: NASA, Artist’s depiction of an active Sun that has released a Coronal Mass Ejection. CMEs are magnetically generated solar phenomenon that can send billions of tons of solar particles, or plasma, into space that can reach Earth one to three days later and affect electronic systems in satellites and on the ground.